The Biology Book: From the Origin of Life to Epigenetics, 250 Milestones in the History of Biology (2015)

Albumin From Rice

2011

Albumin is the most abundant plasma protein in mammals and constitutes 50–55 percent of plasma proteins in humans. Produced in the liver, it serves as a carrier in the blood for hormones, fat-digesting and absorbing bile salts, bilirubin, and blood clotting proteins. Albumin’s most important function is to regulate blood volume by pulling water into the circulatory system—in particular, the capillaries. It is medically used as a plasma expander for the treatment of shock caused by excessive blood loss and severe burns, as well as in combat settings to stabilize the wounded until whole blood is available. Shock results from an inadequate supply of blood-carried oxygen from reaching the cells, causing them irreversible consequences. It is also used in the production of drugs and vaccines.

Human serum albumin (HSA) is extracted from human blood plasma, the liquid component of blood, but with an annual worldwide demand of some 500 tons (500,000 kilograms), natural sources are in short supply. Difficulties have been encountered producing synthetic or laboratory versions of HSA. More recent attempts to produce HSA have used the tools of genetic engineering. The challenge is to develop a high-yield/low-cost system, producing a product with a minimal risk of causing allergic reactions. Past efforts to grow albumin in potato plants and tobacco leaves have not been satisfactory because of low yields.

The rice genome was sequenced in 2005. In 2011, Daichong Yang and his research colleagues in Wuhan, China, have reported successfully growing HSA in rice (Oryza sativa) after using bacteria (Agrobacterium) to insert a gene for encoding HSA. The gene is activated during seed production, resulting in the albumin protein being stored in rice grain with nutrients used to nourish the germinating plant embryo. Comparison of the rice- and human-derived HSA revealed that they were chemically and physically identical, with the same 585-amino-acid sequence and three-dimensional shape, in addition to being biologically equivalent in rats. Around 0.1 oz (2.8 grams) of HSA were produced from 2.2 lbs (1 kg) of brown rice, making this process highly cost-effective, with a virtually unlimited supply.